A progressive addition lens is widely used in general due to its advantages such as that it is not easily recognized as a presbyopia spectacle lens from appearance although it actually is, and that it allows a wearer to clearly look continuously from a far distance to a near distance without discontinuity.
However, it is difficult to design a progressive addition lens because it is necessary to arrange a plurality of visual fields within a limited lens area without interposing a boundary between the plurality of visual fields, the plurality of visual fields being: a visual field for viewing far distance, a visual field for viewing near distance, and a visual field for viewing medium distance. For this reason, it is widely known that the progressive addition lens has its particular disadvantages such as that each visual field is not always sufficiently wide, and that there is a region mainly in a side visual field which causes the wearer to feel distortion or sway of an image.
To overcome these disadvantages, many prior arts have been proposed since long time ago. However, most of these prior arts are related to design technique for obtaining more preferred power distribution or astigmatism distribution depending on individual prescribed power and wear state, and relatively few of these prior arts are made to improve binocular vision of right and left eyes (see Patent Document 1 to 4).
Herein, the term “to improve binocular vision of right and left eyes” mainly means suitably arranging a near region and an intermediate region to obtain good binocular near vision and binocular intermediate vision.
In the aforesaid prior arts, the art disclosed in Patent Document 1 is a technique in which one sides of two kinds of lenses having bilaterally symmetric design are replaced with each other to form a lens having bilaterally asymmetric design, and the lens is rotated by about 10° due to convergence of near vision and set into a frame so that the astigmatism distribution in horizontal direction is bilaterally symmetrical. Further, the art disclosed in Patent Document 2 is a technique relating to design of a progressive addition lens in which the near vision region is bilaterally symmetric about the principal line of vision. Further, the art disclosed in Patent Document 3 is a technique relating to design of a progressive addition lens in which the astigmatism distribution of the near vision region is bilaterally asymmetric about the principal line of vision, in which the astigmatism distribution is denser on the nose side and thinner on the ear side. Further, the art disclosed in Patent Document 4 is a technique relating to a progressive addition lens in which the distortion of the near vision region in vertical direction is bilaterally asymmetric about the principal line of vision, in which the distortion is greater on the nose side and smaller on the ear side.